QmlDesigner: Add content item hack

There is no stand content item interface, so try to work around to enable
snapping and anchoring.

Change-Id: Ib2eaf0d6c35e3ba289dd7d55b2ba4c064ad40748
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>

share/qtcreator/qml/qmlpuppet/qml2puppet/instances/objectnodeinstance.cpp

@@ -245,6 +245,11 @@ QTransform ObjectNodeInstance::transform() const
     return QTransform();
 }
 
+QTransform ObjectNodeInstance::contentTransform() const
+{
+    return QTransform();
+}
+
 QTransform ObjectNodeInstance::customTransform() const
 {
     return QTransform();